<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <link rel="stylesheet" id="linkid" type="text/css" href="4-1.css">
    <script>
        function huanfu1() {
            var o = document.getElementById('linkid');
            o.href = "4-1.css";
        }
        function huanfu2() {
            var o = document.getElementById('linkid');
            o.href = "4-2.css";
        }
    </script>
</head>
<body>
<button onclick="huanfu1()">皮肤1</button>
<button onclick="huanfu2()">皮肤2</button>
<div class="container">
    <div class="header">网站头部</div>
    <div class="left1">左</div>
    <div class="right1">右</div>
    <div class="left2 clearfix">左</div>
    <div class="center2">中</div>
    <div class="right2">右</div>
    <div class="footer">底部</div>
</div>
</body>
</html>